1. Field of the Invention
The present invention generally relates to mobile Internet. More particularly, the present invention relates to a bridge-based cellular Ethernet system for providing a high-speed handover service by a simple and efficient signaling procedure and a handover processing method therefore.
2. Description of the Related Art
At the present time, mobile Internet technology covers 3rd Generation (3G) and 4th Generation (4G) cellular systems based on the Public Land Mobile Network (PLMN) and Portable Internet (PI) or Wireless Broadband (WiBro) for Internet Protocol (IP)-based packet transmission. For ultra high-speed data communications and maximal use efficiency, a variety of standards for the mobile Internet have been proposed.
FIG. 1 illustrates the configuration of a Fast Mobile IPv6 network. In addition, FIG. 2 is a diagram illustrating a signal flow for an exemplary handover procedure in the Fast Mobile IPv6 network. Fast Mobile IPv6 is a protocol proposed to minimize the handover latency of Mobile IPv6. Some terminology of Fast Mobile IPv6 is first given below.                Mobile Node (MN): a mobile node supporting IPv6.        Access Point (AP): a Layer 2 (L2) entity connected to an IP subnet, for providing wireless connectivity to the MN.        AP-ID: an L2 address of an AP.        Access Router (AR): a default router connected to the MN.        Previous Access Router (PAR): an old AR that the MN is attached to before handover.        New Access Router (NAR): a new AR that the MN is attached to after the handover.        Previous Care-of-Address (PCoA): an MN's CoA that is valid in the subnet of the PAR.        New CoA (NCoA): an MN's CoA that is valid in the subnet of the NAR.        Router Solicitation for Proxy Advertisement (RtSolPr): a message from the MN to the PAR, requesting information about neighbor APs before the handover.        Proxy Router Advertisement (PrRtAdv): a message from the PAR to the MN in response to the RtSolPr message, containing the neighbor AP information. The PrRtAdv message is sent without the RtSolPr message in case of a network-initiated handover.        (AP-ID, AR-info) tuple: the L2 address and IP address of an AR to which an AP with an AP-ID is connected. This tuple contains a valid prefix. AR-info is composed of [Router's L2 address, Router's IP address, Prefix].        Assigned Addressing: a particular type of NCoA configuration in which the NAR assigns an IPv6 address to the MN.        Fast Binding Update (FBU): a message from the MN to the PAR, instructing the PAR to redirect the MN's packets towards the NAR.        Fast Binding acknowledgement (FBack): a response message for the FBU message from the PAR to the MN.        Fast Neighbor Advertisement (FNA): a message from the MN to the NAR, announcing attachment.        Handover Initiate (HI): a message from the PAR to the NAR to initiate a handover.        Handover Acknowledge (HAck): a message from the NAR to the PAR in response to the HI message.        
Referring to FIG. 1, Access Routers (Ars) 103 and 104 forming a plurality of subnets are connected to a core IP network 10 with a plurality of routers 101 and 102. As an MN 115 moves from the Previous Access Router (PAR 103) to the New Access Router (NAR) 104, a handover is triggered. The handover procedure will be described with reference to FIG. 2.
Referring to FIG. 2, for handover, the mobile node (MN) first requests information about at least one Access Point (AP) detected in L2 to its PAR by sending a Router Solicitation for Proxy Advertisement (RtSolPr) message in step 201 and the PAR replies with a Proxy Router Advertisement (PrRtAdv) message with {AP-ID, AR-info} in step 202. ARs may periodically exchange information about APs attached to them with one another.
Upon receipt of the PrRtAdv message, the MN sets a new NCoA for use in a new AP to which that it will be attached according to the {AP-ID, AR-info} in step 203. When a handover event actually occurs in L2, the MN sends an FBU message to the PAR in step 204. Because the Fast Binding Update (FBU) includes the New CoA (NcoA), the PAR stores binding information for the NCoA and the PCoA and forwards packets directed to the MN toward the NAR though a tunnel which has been established with the NAR using the biding information in steps 209, 210 and 211. If possible, preferably but not necessarily, the FBU message is sent while the MN is still connected to the PAR. If not possible, the FBU message is sent after the MN is attached to the NAR. The PAR sends an FBack message to the MN in response to the FBU message in step 207.
The MN operates in different modes depending on whether the FBack message is received by the MN when it is attached to the PAR or the NAR. In the former case (predictive fast handover), which means that a tunnel has already been established before the MN is attached to the NAR, the MN sends an FNA to the NAR immediately after the attachment and receives buffered packets from the NAR in steps 212 and 214. Then the MN sends a Binding Update message to a Home Agent/Core Network (HA/CN) in step 215. The HA/CN replies with a Binding Ack message and updates binding information in step 216.
In this mode, upon receipt of the FBU message, the PAR sends a Handover Initiate (HI) message to the NAR to find out whether the MN-created NCoA included in the FBU message is acceptable in the NAR in step 205. If the NCoA is already in use, the NAR generates a new NCoA and sends a HAck message with the NCoA to the PAR in step 206 and the PAR sends an FBack message with the new NCoA to the MN in step 207. Therefore, the MN should use the new NCoA after the attachment to the NAR. On the other hand, if the MN-created NCoA is acceptable, no NCoA is included in the HAck message and the FBack message.
FIG. 3 is a diagram illustrating a signal flow for another exemplary handover procedure in the Fast Mobile IPv6 network illustrated in FIG. 1.
Referring to FIG. 3, the MN sends an RtSolPr message to the PAR in a similar manner as in the handover procedure depicted in FIG. 2 in step 301. After receiving a PrRtAdv message from the PAR in step 302 and setting a new NCoA for use in the new AP in step 303, the MN fails to receive an FBack message (reactive fast handover). This particular case occurs when the MN does not send an FBU message while it is connected to the PAR or a handover has occurred before receiving an FBack message in response to a transmitted FBU message.
Since the MN cannot determine whether or not the PAR has processed the FBU message successfully due to the reception failure of the FBack message, it sends an FBU message (initial transmission or retransmission) to the NAR immediately after its attachment to the NAR in step 305. The FBU message is carried in an FNA message such that the NAR can send packets immediately after processing the FBU message and determine whether the NCoA is acceptable. The NAR checks the validity of the NCoA set in the FBU message in step 306. If the NCoA is already in use, the NAR discards the packet and sends to the MN a Router Advertisement message with a Neighbor Advertisement Acknowledge (NAACK) option in step 307. This message contains an NCoA that the MN will use in the NAR.
Hence, the MN sends a new FBU message using the new NCoA to the NAR in steps 308, 309 and 310. The NAR forwards the FBU message to the PAR in step 311 and the PAR sends an FBack message to the NAR in step 312. Therefore, the PAR redirects the MN's packets to the NAR in step 313 and 314 and the NAR forwards the packets to the MN in step 315. Subsequently, binding information regarding the MN is updated in the HA/CN in steps 316 and 317.
As described above, although Fast Mobile IPv6 minimizes the handover latency of Mobile IPv6, a drawback with Fast Mobile IPv6 is that a new IP should be allocated each time the MN moves between ARs in view of the nature of an IP-layer handover protocol and thus particular signaling packets should be exchanged, thereby causing a delay. Especially when an NCoA set by the MN is not valid during a reactive handover, an additional signaling packet is needed to allocate a new NCoA, thereby adding to the delay.